Analysis of streambed temperatures in ephemeral channels to determine streamflow frequency and duration

Spatial and temporal patterns in streamflow are rarely monitored for epheme ral streams. Flashy, erosive streamflows common in ephemeral channels creat e a series of operational and maintenance problems, which makes it impracti cal to deploy a series of gaging stations along ephemeral channels. Streamb ed temperature is a robust and inexpensive parameter to monitor remotely, l eading to the possibility of analyzing temperature patterns to estimate str eamflow frequency and duration along ephemeral channels. A simulation model was utilized to examine various atmospheric and hydrological upper boundar y conditions compared with a series of hypothetical temperature-monitoring depths within the streambed. Simulation results indicate that streamflow ev ents were distinguished from changing atmospheric conditions with greater c ertainty using temperatures at shallow depths (e.g,, 10-20 cm) as opposed t o the streambed surface. Three ephemeral streams in the American Southwest were instrumented to monitor streambed temperature for determining the accu racy of using this approach to ascertain the long-term temporal and spatial extent of streamflow along each stream channel. Streambed temperature data were collected at the surface or at shallow depth along each stream channe l, using thermistors encased in waterproof, single-channel data loggers tet hered to anchors in the channel. On the basis of comparisons with site info rmation, such as direct field observations and upstream flow records, diurn al temperature variations successfully detected the presence and duration o f streamflow for all sites.